Semiconductor light emitting element

ABSTRACT

According to one embodiment, a semiconductor light emitting element includes a light emitting layer, a current spreading layer of a first conductivity type, and a pad electrode. The light emitting layer is capable of emitting light. The current spreading layer has a first surface and a second surface. The light emitting layer is disposed on a side of the first surface. A light extraction surface having convex structures of triangle cross-sectional shape and a flat surface which is a crystal growth plane are included in the second surface. The pad electrode is provided on the flat surface. One base angle of the convex structure is 90 degrees or more.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2010-276839, filed on Dec. 13,2010; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a semiconductor lightemitting element.

BACKGROUND

High light extraction efficiency (efficiency of extracting light emittedfrom a light emitting layer to the outside of a semiconductor lightemitting element) is required for semiconductor light emitting elementsused in illumination devices, display devices, traffic signals, etc.

By providing a reflection layer under a light emitting layer in asemiconductor light emitting element having a stacked structure, it ispossible to increase the light extraction efficiency of thesemiconductor light emitting element. In addition, by forming fineuneven surface on a light extraction surface provided on a side oppositeto the reflection layer via the light emitting layer, it is possible tofurther increase the light extraction efficiency. However, it isdifficult to sufficiently increase the light extraction efficiency withthe uneven surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a semiconductor lightemitting element according to a first embodiment of the invention;

FIG. 2A is a schematic perspective view of a light extraction surface,and FIG. 2B is a schematic view of convex structures withcross-sectional shape of triangle taken along line K-K;

FIG. 3A is a SEM photograph of a cross-section along line K-K (directionDC) of the light extraction surface, FIG. 3B is a SEM photograph asviewed from directly above the light extraction surface (direction DU),FIG. 3C is a SEM photograph as viewed from the upward direction in 40degrees obliquely on the front side DF₄₀, and FIG. 3D is a SEMphotograph as viewed from the upward direction in 40 degrees obliquelyon the lateral side DS₄₀;

FIG. 4A is a schematic view illustrating a light extraction directionwhen both base angles of the convex structures are acute angles, andFIG. 4B is a schematic view illustrating a light extraction direction ina case of the first embodiment wherein one base angle of the convexstructures is obtuse angle;

FIG. 5 is a schematic cross-sectional view of a semiconductor lightemitting element according to a variation of the first embodiment;

FIG. 6A is a cross-sectional SEM photograph of a convex structure of asemiconductor light emitting element according to a second embodiment,FIG. 6B is a schematic cross-sectional view before forming a convexstructure, FIG. 6C is a schematic cross-sectional view after forming aconvex structure portion, and FIG. 6D is a schematic cross-sectionalview after forming a pillar;

FIG. 7A is a schematic cross-sectional view illustrating a structure ofa current spreading layer of a semiconductor light emitting elementaccording to a third embodiment, FIG. 7B is a schematic cross-sectionalview after forming a convex structure, and FIG. 7C is a schematiccross-sectional view after forming a pillar; and

FIG. 8A is a first variation of the third embodiment, FIG. 8B is asecond variation thereof, and FIG. 8C is a third variation thereof.

DETAILED DESCRIPTION

In general, according to one embodiment, a semiconductor light emittingelement includes a light emitting layer, a current spreading layer of afirst conductivity type, and a pad electrode. The light emitting layeris capable of emitting light. The current spreading layer has a firstsurface and a second surface. The light emitting layer is provided on aside of the first surface. A light extraction surface having convexstructures with cross-sectional shape of triangle and a flat surfacewhich is a crystal growth plane are included in the second surface. Thepad electrode is provided on the flat surface. One base angle of theconvex structure is 90 degrees or more.

Hereinafter, embodiments of the invention will be described withreference to the drawings.

FIG. 1 is a schematic cross-sectional view of a semiconductor lightemitting element according to a first embodiment of the invention.

The semiconductor light emitting element is provided with a padelectrode 42, a first stacked structures 30 made of a semiconductor, alight emitting layer 40, a second stacked structure 20 made of asemiconductor, and a support substrate 10.

In FIG. 1, although the semiconductor stacked structure including thefirst stacked structure 30, the light emitting layer 40, and the secondstacked structure 20 is made of an InAlGaP-based material represented bythe composition formula In_(x)(Al_(y)Ga_(1−y))_(1−x)P (0≦x≦1 and 0≦y≦1),the material is not limited thereto, and may be configured with anAlGaAs-based material represented by the composition formulaAl_(x)Ga_(1−x)As (0≦x≦1), an InGaAlAsP-based material represented by thecomposition formula of In_(x)(Al_(y)Ga_(1−y))_(1−x)As_(z)P_(1−z) (0≦x≦1,0≦y≦1 and 0≦z≦1), and an InGaAlN-based material represented by thecomposition formula In_(x)Al_(y)Ga_(1−x−y)N (0≦x≦1, 0≦y≦1, and x+y≦1),or a combination of these materials.

The first stacked structure 30 has a first conductivity type andincludes a cladding layer 31 made of In_(0.5)Al_(0.5)P, a currentspreading layer 32, and a contact layer 39 made of GaAs. Although thefirst conductivity type is an n-type in this embodiment, the inventionis not limited thereto.

By configuring the light emitting layer 40 to have a MQW (Multi QuantumWell) structure including well layers and barrier layers which are madeof In_(x)(Al_(y)Ga_(1−y))_(1−x)P (0≦x≦1 and 0≦y≦1), it is possible toincrease an internal quantum efficiency of emission light and also tohave a wavelength range of a visible light.

The second stacked structure 20 has a second conductivity type and isprovided between the light emitting layer 40 and the support substrate10. The second stacked structure 20 includes a contact layer 21 made ofGaP, AlGaAs, or the like, an intermediate layer 24 made of InGaAlP orthe like, and a cladding layer 25 made of In_(0.5)Al_(0.5)P or the like,in this order from the side of the support structure 10.

The support substrate 10 includes a substrate 11 made of Si or the like,a bonding metal layer 12 provided in an upper portion of the substrate11, a lower electrode 18 provided on the rear surface of the substrate11, an ITO (Indium Tin Oxide) film 14 provided on the bonding metallayer 12, and a current blocking layer 15 made of an insulator such asSiO₂ selectively provided on the ITO film 14. Light emitted downwardfrom the light emitting layer 40 is reflected by the bonding metal layer12, the current blocking layer 15, and the like, and the light is easilyextracted from the light extraction surface.

Here, the first stacked structure 30, the light emitting layer 40, andthe second stacked structure 20 are formed on a GaAs substrate, forexample, by epitaxial growth technique. Subsequently, an insulating filmsuch as SiO₂ is formed on the surface of the contact layer 21 and isleft in a region under the pad electrode 42 and in a part for blockingcurrent flow as the current blocking layer 15, by lithography pattering.The ITO film 14 and a metal layer 12 a such as Au are formed on thepatterned dielectric film. The GaAs substrate side having the metallayer 12 a on the surface and the substrate 11 surface having a metalfilm 12 b including Au or the like on the surface are faced each other,and heated and pressured to bond two substrate in one wafer state, andthus, the bonding metal layer 12 is formed. Here, a broken lineindicates a bonded interface.

The current spreading layer 32 includes a first surface 32 a and asecond surface and has the first conductivity type. The light emittinglayer 40 is provided on the first surface 32 a side of the currentspreading layer 32. Furthermore, the second surface includes a lightextraction surface 32 d having many convex structures and a flat surface32 b which is a surface of a crystal growth plane. Here, the padelectrode 42 is provided on the flat surface 32 b of the currentspreading layer 32 via the contact layer 39.

FIG. 2A is a schematic perspective view of the light extraction surfaceas viewed obliquely from above, and FIG. 2B is a schematiccross-sectional view taken along line K-K.

The convex structure 32 c with cross-sectional shape of triangleprovided on the current spreading layer 32 protrudes along line K-K andhas a first side surface 32 e and a second side surface 32 f. The firstside surface 32 e has an angle α and the second side surface 32 f has anangle β with respect to a plane parallel to a crystal growth plane whichis the bottom portion of the convex structure 32 c. The angle α and theangle β are defined as “base angles” of the convex structure. In thefirst embodiment, one of the two base angles α and β is 90 degrees ormore. In the embodiment shown in FIGS. 2A and 2B, the base angle β is 90degrees or more. It is possible to form such cross-section of the convexstructure 32 c by tilting the crystal growth plane using a tiltedsubstrate and selecting an etching solution appropriately. A formationmethod thereof will be explained in detail below.

FIG. 3A is a SEM photograph of a cross-section along line K-K (directionDC) of the light extraction surface, FIG. 3B is a SEM photograph asviewed from directly above the light extraction surface (direction DU),FIG. 3C is a SEM photograph as viewed from the upward direction in 40degrees obliquely on the front side DF₄₀, and FIG. 3D is a SEMphotograph as viewed from the upward direction in 40 degrees obliquelyon the lateral side DS₄₀.

In FIGS. 3A to 3D, the crystal growth plane is tilted at 15 degrees fromthe (−100) plane toward the [011] direction. That is, FIG. 3A shows across-section of the convex structure 32 as viewed from the direction DCof FIG. 2A, and corresponds to the schematic cross-sectional view ofFIG. 2B. The cross-section in FIG. 3A is the (011) plane. Furthermore,FIG. 3B shows the light extraction surface as viewed from directly abovethe light extraction surface (direction DU), FIG. 3C shows the convexstructure 32 c as viewed from a direction of 40 degrees obliquely upwardon the front side (DF₄₀), and FIG. 3D shows the convex structure 32 cfrom a direction of 40 degrees obliquely upward on the just lateral side(DS₄₀).

FIG. 4A is a schematic view illustrating a light extraction directionwhen both of the base angles have acute angles, and FIG. 4B is aschematic view illustrating a light extraction direction in a case ofthe first embodiment.

In FIG. 4A, emission light g1 from the light emitting layer enters asecond side surface 132 b of a convex structure 132 in an incident angleθi1. When the incident angle θi1 is smaller than a critical angle θc,transmitted light g1 t and reflected light g1 r are generated. When theincident angle θi1 is larger than the critical angle θc, totalreflection occurs. When the reflected light g1 r enters a first sidesurface 132 a and an incident angle θi2 is smaller than the criticalangle θc, transmitted light g1 rt and reflected light g1 rr aregenerated. When the incident angle θi2 is larger than the critical angleθc, it becomes difficult to extract the emission light further morebecause of the total reflection. When light extraction efficiency in acase without convex structures are defined to be 100%, the lightextraction efficiency was 130% in the case where the convex structuresof FIG. 4A were provided. Here, when the refractive index of the currentspreading layer 32 is assumed to be 3.2 and the refractive index of asealing layer covering the surface of a light emitting element isassumed to be 1.4, the critical angle θc becomes approximately 26degrees.

In FIG. 4B, emission light G1 from the light emitting layer enters afirst side surface 32 d of the convex structure 32 c, and, when theincident angle θi1 is smaller than the critical angle θc, transmittedlight G1 t and reflected light G1 r are generated. Here, when theincident angle θi1 is larger than the critical angle θc, the totalreflection occurs. When the reflected light G1 r enters a second sidesurface 32 e and the incident angle θi2 is smaller than the criticalangle θc, transmitted light G1 rt and reflected light G1 rr aregenerated. Further, when the reflected light G1 rr enters the first sidesurface 32 d and the incident angle θi3 is smaller than the criticalangle θc, the reflected light G1 rr is transmitted.

In the first embodiment, since the surface area of the convex structure32 c can be increased, the number of reflections within the convexstructure 32 c becomes larger than that in the case of the shape shownin FIG. 4A and thus more emission light can be extracted. Accordingly,it is possible to increase the light extraction efficiency. The lightextraction efficiency was 145% in a semiconductor light emitting elementhaving the convex structures 32 c as shown in FIG. 4B. Furthermore, ithas been found from an experiment by the inventors that the lightextraction efficiency can be increased to 150% compared with the lightextraction efficiency of a light emitting element having a flat lightextraction surface without convex structures when a range of the baseangle α of the first side plane 32 d is set to be a range from 35degrees or more to 45 degrees or less.

When the light extraction surface is made of one ofIn_(x)(Al_(y)Ga_(1−y))_(1−x)P (0≦x≦1 and 0≦y≦1), Al_(x)Ga_(1−x)As(0≦x≦1), In_(x)(Al_(y)Ga_(1−y))_(1−x)AszP_(1−z) (0≦x≦1, 0≦y≦1 and0≦z≦1), and In_(x)Al_(y)Ga_(1−x−y)N (0≦x≦1, 0≦y≦1, and x+y≦1), it iseasy to form the convex structures 32 c with the base angle ≧90 degreesby setting a crystal growth plane tilted from the {100} plane with anangle between 10 degrees and 20 degrees. Furthermore, it is morepreferable to set a tilt direction from the {100} plane to be an A planedirection which is the (111) group-III plane or a B plane directionwhich is the (111) group-V plane. Note that, the {100} plane includesequivalent planes represented by (100), (010), (001), (−100), (0-10), or(00-1).

On the wafer surface having such a tilt angle described above, theconvex structures 32 c with the base angle≧90 degrees as shown in FIG.2B can be formed by using a wet etching method. They are so-called frostconcave-convex structures. Crystal degradation by the wet etchingprocess is suppressed compared with the dry etching process such as anRIE (Reactive Ion Etching) method. Thus, it is easy to keep a highluminance even in a long term operation with the convex structuresformed by the wet etching process. Here, it is preferable to set theheight of the convex structures 32 c to be equal to or larger than 20 nmor the like, for example. It is possible to use a water solutioncontaining hydrochloric acid, acetic acid, and hydrofluoric acid or thelike, for example, for the wet etching solution.

The current spreading layer 32 can spread carriers injected from the padelectrode 42 in the plane of the light emitting layer 40. The contactlayer 39 provided between the current spreading layer 32 and the padelectrode 42 is made of GaAs. The contact layer 39 is removed from thesecond surface of the current spreading layer 32 only in a region wherethe convex structures 32 c are formed to provide make the desired lightextraction surface 32 d. The current spreading layer 32 is etched byusing the contact layer 39 as a frost mask to form the frost having theconvex structure 32 c. In FIG. 1, although the contact layer 39 remainsunder the pad electrode 42, the pad electrode 42 can be formed directlyon the flat current spreading layer 32 by removing the GaAs layer.

Furthermore, when a narrow-line electrode having a width of 10 μm orless, for example, is provided around the pad electrode 42, thenarrow-line electrode can be provided on the GaAs layer. Alternatively,a self-aligned structure in which the narrow-line electrode is patternedon the GaAs layer and then GaAs is etched by using the narrow-lineelectrode as a mask can be employed. In this case, the frostconcave-convex structures can be formed uniformly close to the vicinityof the narrow-line electrode and it is possible to increase the lightextraction efficiency further more.

FIG. 5 is a schematic cross-sectional view of a semiconductor lightemitting element according to a variation of the first embodiment.

The semiconductor light emitting element is provided with a padelectrode 42, a first stacked structure 30 made of a semiconductor, alight emitting layer 40, a second stacked structure 20 made of asemiconductor, and a support substrate 10.

The first stacked structure 30 has the first conductivity type andincludes a cladding layer 31 made of In_(0.5)Al_(0.5)P, a currentspreading layer 32, and a contact layer 39 made of GaAs. Although thefirst conductivity type is an n-type, the invention is not limitedthereto. By configuring the light emitting layer 40 to have a MQWstructure including well layers and barrier layers which are made ofIn_(x)(Al_(y)Ga_(1−y))_(1−x)P (0≦x≦1 and 0≦y≦1), it is possible toincrease an internal quantum efficiency of the emission light and alsoto set the wavelength arbitrarily in a visible light range. The secondstacked structure 20 has the second conductivity type, and a claddinglayer 25 which is made of In_(0.5)Al_(0.5)P or the like and providedbetween the light emitting layer 40 and a substrate 12 made of GaAs anda distributed Bragg reflector (DBR) layer 23 which is a multilayer filmmade of InGaAlP, GaAlAs or the like and selectively reflects lighthaving a wavelength of the emission light from the light emitting layer40 are formed on the substrate 12. The light emitted downward from thelight emitting layer 40 is reflected by the DBR layer 23 and can beextracted from above. Furthermore, the rear surface of the substrate 12is provided with a lower electrode 18.

The current spreading layer 32 includes a first surface 32 a and asecond surface 32 b, and has the first conductivity type. The lightemitting layer 40 is provided on the first surface 32 a side of thecurrent spreading layer 32. Moreover, the second surface includes alight extraction surface 32 d having multiple convex structures and aflat surface 32 b which is a crystal growth plane. Here, the padelectrode 42 is provided, for example, via the contact layer 39 on theflat surface 32 b of the current spreading layer 32. It is also possibleto employ a structure in which current does not flow directly under thepad electrode 42 by providing a current blocking layer between the padelectrode 42 and the contact layer 39. Also in the variation, it ispossible to increase the light extraction efficiency up to 145% byforming the convex structures 32 c as shown in FIG. 4B for the lightextraction surface of the current spreading layer 32, in comparison witha case where convex structures are not formed. Furthermore, it has beenfound from an experiment by the inventors that the light extractionefficiency can be increased to 150% when the base angle α of the firstside plane 32 d is set between 35 degrees and 45 degrees, compared withthat of a semiconductor light emitting element having a flat lightextraction surface without convex structures. When the light extractionsurface is made of In_(x)(Al_(y)Ga_(1−y))_(1−x)P (0≦x≦1 and 0≦y≦1), itis easy to form the convex structure 32 c by using a GaAs substratetilted from the {100} plane with an angle range between 10 degrees and20 degrees for the substrate 12. Furthermore, it is more preferable toset a tilt direction from the {100} plane to be the (111) group-IIIplane direction or the (111) group-V plane direction.

FIG. 6A is a cross-sectional SEM photograph of a convex structure of asemiconductor light emitting element according to a second embodiment,FIG. 6B is a schematic cross-sectional view before forming a convexstructure, FIG. 6C is a schematic cross-sectional view after forming theconvex structure, and FIG. 6D is a schematic cross-sectional view afterforming a pillar.

A current spreading layer 32 includes a first surface and a secondsurface and has the first conductivity type. A light emitting layer isprovided on the first surface side. On the second surface, there areprovided a light extraction surface including a pillar 34 a, a convexstructure 33 a provided on the pillar 34 a, and a bottom portion 34 bprovided around the pillar 34 a, and a flat surface having a surface ofa crystal growth plane. At least a part of the bottom surface 33 b ofthe convex structure 33 a protrudes from a sidewall 34 c of the pillarpart 34 a in the lateral direction. The light extraction efficiency was140% in a semiconductor light emitting element having the convexstructures 33 a as shown in FIG. 6A. A head portion including the bottomsurface 33 b of the convex structure 33 a which protrudes from thepillar 34 a has a shape like a key head portion and realizes a highadhesion strength in which a sealing layer made of silicone resin or thelike and the current spreading layer 32 are interlocked with each other.When the convex structure 33 a is not provided with the head portionhaving a key shape, the sealing layer may be easily peeled off from thecurrent spreading layer and the light output is reduced because of thelight output direction shift.

At the bottom portion of the convex structure 33 a provided in a firstlayer 33, a first side surface 33 e and a second side surface 33 f haveangles α and β, respectively with respect to a plane parallel to thecrystal growth plane. The angle α and the angle β are defined as “baseangles”.

As shown in FIG. 6B, the current spreading layer 32 includes the firstlayer 33 formed by crystal growth on an inclined substrate and a secondlayer 34, and the composition formula is represented byIn_(x)(Al_(y)Ga_(1−y))_(1−x)P (0≦x≦1 and 0≦y≦1). The first layer 33 hasan Al composition ratio y of 0.3. Furthermore, the second layer 34 hasan Al composition ratio y of 0.7 which is higher than the compositionratio y of the first layer 33. The etching rate of the first layer 33 isassumed to be approximately five times larger than that of the secondlayer 34. The protruding portion 33 a has a saw-tooth-like cross-sectionin a state of just etching shown in FIG. 6B. The pillar part 34 a isformed by additional etching in the second layer 34 having a higheretching rate as shown in FIG. 6D and the etching is finished when thepillar part 34 a comes to have a desired height from the bottom plane 34f of the bottom part 34 b. In this manner, the convex structure 33 ahaving a key shape is provided for the current spreading layer 32, andthus it is possible to improve the adhesiveness between the surface of asemiconductor light emitting element and the sealing layer.

In the second embodiment, the convex structure 33 a and the pillar 34 aincrease the surface area of the light extraction surface 32 d toincrease the number of light reflections, and thus, the light extractionefficiency can be increased. Furthermore, it has been found from anexperiment by the inventors that the luminance can be increased when theAl composition ratio y of the current spreading layer 32 has a highervalue of 0.7. Accordingly, the portion other than the convex structure33 a is configured with the second layer 34 which has a higher Alcomposition ratio y of 0.7.

FIG. 7A is a schematic cross-sectional view illustrating a structure ofa current spreading layer of a semiconductor light emitting elementaccording to a third embodiment, FIG. 7B is a schematic cross-sectionalview after forming a convex structure, and FIG. 7C is a schematiccross-sectional view after forming a pillar.

In the third embodiment, the current spreading layer 32 includes a firstlayer 33, a second layer 34, a third layer 35, and a fourth layer 36.The first layer 33 has an Al composition ratio y of 0.3 and a thicknessof 600 nm. The second layer 34 has an Al composition ratio y of 0.7 anda thickness of 400 nm. The third layer 35 has an Al composition ratio yof 0.3 and a thickness of 500 nm. Furthermore, the fourth layer 36 hasan Al composition ratio y of 0.7. Here, preferably, the first layer 33has a thickness of 600 nm±200 nm, the second layer 34 has a thickness of400 nm±200 nm, and the third layer 35 has a thickness of 500 nm±200 nm.Furthermore, preferably, the Al composition ratio y of the first layer33 is 0.3±0.15, the Al composition ratio y of the second layer 34 is0.7±0.15, and the Al composition ratio y of the third layer 35 is0.3±0.15.

First, as shown in FIG. 7B, a convex structure 33 a is formed in thefirst layer 33 after etching of 600 nm depth. Subsequently, byadditional etching, a pillar 34 a is formed having a height ofapproximately 600 nm since the etching rate of the second layer 34 isfive times higher than that of the first layer 33. Since the etchingrate of the third layer 35 is approximately one fifth lower than that ofthe second layer 34, the surface of the third layer 35 acts as anetching stop layer, and thus the height of the pillar 34 a can keepaccurately and also stably. By providing the fourth layer 36 having ahigh Al composition ratio y of 0.7, it can be improve the luminance.

FIG. 8A, FIG. 8B, and FIG. 8C are schematic cross-sectional views oflight extraction surfaces of a first variation, a second variation, anda third variation of the third embodiment, respectively.

In FIG. 8A, the Al composition ratio y of a second layer 34 is inclinedalong the depth direction from 0.3 to 0.7. As a result, a pillar 34 abecomes finer in a deeper part. Therefore, the adhesiveness is improvedbetween a sealing layer and a current spreading layer 32.

In FIG. 8B, the Al composition ratio y of the second layer 34 is reducedfrom 0.7 to 0.3 along with the depth. As a result, the pillar 34 abecomes thicker along with the depth. In this case, light G11 enters asidewall 34 d of the pillar 34 a to be totally reflected, and thenbecomes output light G11 a from the convex structure 33 a. Furthermore,light G13 enters a sidewall 34 e after totally reflected by the sidewall 34 d and generates transmitted light G13 a and reflected light. Thereflected light generates output light G13 b and reflected light fromthe sidewall 34 d. In this manner, reflection and transmission arerepeated, and it is possible to increase the light extractionefficiency. Moreover, light G12 also can be output from an exposedsurface 35 a of a third layer 35.

FIG. 8C shows a convex structure 33 a having a saw-tooth-shapedcross-section as in the second embodiment. That is, when the convexstructure 33 a is made of In_(x)(Al_(y)Ga_(1−y))_(1−x)P (0≦x≦1 and0≦y≦1), a plane tilted from the {100} plane with an angle between 10degrees and 20 degrees, for example, is used as the crystal growthplane. In addition, more preferably, the tilt angle from the {100} planeis the (111) group-III plane direction or the (111) group-V planedirection.

Furthermore, the base angle β of the convex structure 33 a is configuredto be 90 degrees or more. In the emission light, light G10 which haspassed through a pillar 34 a and entered the convex structure 33 aenters a first side surface 33 b and branches into transmitted light G10a toward the outside and reflected light. The reflected light enters asecond side surface 33 c and generates transmitted light G10 b andreflected light. The reflected light at the second side surface 33 centers the first side surface 33 b again and becomes transmitted lightG10 c and reflected light. The reflected light is extracted from thesecond side surface 33 c as transmitted light G10 d. In this manner,reflection and transmission are repeated many times and thus, the lightextraction efficiency can be increased. Furthermore, light which hasentered the sidewall from the inside of the pillar 34 a enters theconvex structure 33 a and can be extracted to the outside afterrepeating transmission and reflection. Accordingly, the light extractionefficiency can be increased up to 145% in comparison with the casewithout convex structures. Further, it has been found from an experimentby the inventors that the light extraction efficiency can be improved to150% when the other base angle α of the convex structure 33 a is between35 degrees and 45 degrees, in comparison with the light extractionefficiency of a light emitting element having a flat light extractionsurface without convex structures.

As described above, according to the first to third embodiments and theaccompanying variations, it is possible to provide a semiconductor lightemitting element having improved light extraction efficiency bycontrolling the shape of the convex structures. These light emittingelements can be widely used in illumination devices, display devices,traffic signals, etc.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modification as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A semiconductor light emitting element,comprising: a light emitting layer capable of emitting light; and acurrent spreading layer of a first conductivity type having a firstsurface and a second surface, wherein, the light emitting layer isprovided on the first surface, the second surface including a lightextraction region and a flat contact region, the light extraction regionhaving a plurality of convex structures with triangle cross-sectionalshape, a bottom portion of each of the plurality of convex structureswith triangle cross-sectional shape is parallel to a crystal growthplane, wherein the plurality of convex structures with trianglecross-sectional shape is below the flat contact region at the secondsurface of the current spreading layer, one of base angles of each ofthe plurality of convex structures with triangle cross-sectional shapeis more than 90 degrees, the other of the base angles of each of theplurality of convex structures with triangle cross-sectional shape isbetween 35 degrees and 45 degrees, and the current spreading layerincludes one of In_(x)(Al_(y)Ga_(1-y))_(1-x)P (0≦x≦1 and 0≦y≦1),Al_(x)Ga_(1-x)As (0≦x≦1), In_(x)(Al_(y)Ga_(1-y))_(1-x)As_(z)P_(1-z)(0≦x≦1, 0≦y≦1 and 0≦z≦1), and In_(x)Al_(y)Ga_(1-x-y)N (0≦x≦1, 0≦y≦1, andx+y≦1).
 2. The element according to claim 1, wherein the crystal growthplane is tilted from a {100} plane with an angle between 10 degrees and20 degrees.
 3. The element according to claim 2, further comprising: asupport substrate provided on a side of the light emitting layeropposite to the current spreading layer; a layer of a secondconductivity type provided between the light emitting layer and thesupport substrate; and a reflection layer provided between the supportsubstrate and the layer of the second conductivity type and reflectingthe emission light from the light emitting layer, a part of lightreflected by the reflection layer being extracted from the lightextraction surface.
 4. The element according to claim 1, wherein thelight emitting layer and the current spreading layer include a compoundsemiconductor made of group-III elements and group-V elements, and thecompound semiconductor includes at least one ofIn_(x)(AI_(y)Ga_(1-y))_(1-x)P (0≦x≦1 and 0≦y≦1), AI_(x)Ga_(1-x)As(0≦x≦1), In_(x)(AI_(y)Ga_(1-y))_(1-x)AS_(z)P_(1-z) (0≦x≦1, 0≦y≦1 and0≦z≦1), and In_(x)(AI_(y)Ga_(1-x-y))N (0≦x≦1, 0≦y≦1, and x+y≦1).
 5. Theelement according to claim 4, wherein the crystal growth plane is tiltedfrom a {100} plane toward a (111) group-III plane or a (111) group-Vplane.
 6. The element according to claim 4, further comprising: asupport substrate provided on a side of the light emitting layeropposite to the current spreading layer; a layer of a secondconductivity type provided between the light emitting layer and thesupport substrate; and a reflection layer provided between the supportsubstrate and the layer of the second conductivity type and reflectingthe emission light from the light emitting layer, a part of lightreflected by the reflection layer being extracted from the lightextraction surface.
 7. The element according to claim 1, furthercomprising: a support substrate provided on a side of the light emittinglayer opposite to the current spreading layer; a layer of a secondconductivity type provided between the light emitting layer and thesupport substrate; and a reflection layer provided between the supportsubstrate and the layer of the second conductivity type and reflectingthe emission light from the light emitting layer, a part of lightreflected by the reflection layer being extracted from the lightextraction surface.
 8. A semiconductor light emitting element,comprising: a light emitting layer capable of emitting light; and acurrent spreading layer of a first conductivity type having a firstsurface and a second surface, wherein, the light emitting layer isprovided on the first surface, the second surface including a lightextraction region and a flat contact region, the light extraction regionhaving a plurality of convex structures with triangle cross-sectionalshape, a bottom portion of each of the plurality of convex structureswith triangle cross-sectional shape is parallel to a crystal growthplane, wherein the plurality of convex structures with trianglecross-sectional shape is below the flat contact region at the secondsurface of the current spreading layer, a crystal orientation of thecrystal growth plane is tilted from a {100} plane with an angle between10 degrees and 20 degrees, one of base angles of each of the pluralityof convex structures with triangle cross-sectional shape is more than 90degrees, the other of the base angles of each of the plurality of convexstructures with triangle cross-sectional shape is between 35 degrees and45 degrees, and the current spreading layer includes one ofIn_(x)(Al_(y)Ga_(1-y))_(1-x)P (0≦x≦1 and 0≦y≦1), Al_(x)Ga_(1-x)As(0≦x≦1), In_(x)(Al_(y)Ga_(1-y))_(1-x)As_(z)P_(1-z) (0≦x≦1, 0≦y≦1 and0≦z≦1), and In_(x)Al_(y)Ga_(1-x-y)N (0≦x≦1, 0≦y≦1, and x+y≦1).
 9. Theelement according to claim 8, further comprising: a support substrateprovided on a side of the light emitting layer opposite to the currentspreading layer; a layer of a second conductivity type provided betweenthe light emitting layer and the support substrate; and a reflectionlayer provided between the support body and the layer of the secondconductivity type and reflecting the emission light from the lightemitting layer, a part of light reflected by the reflection layer beingextracted from the light extraction surface.
 10. The element accordingto claim 9, wherein the crystal growth plane is tilted from a {100}plane toward a (111) group-III plane or a (111) group-V plane.